Verizon Wireless is experiencing a widespread billing service disruption that has been ongoing for nearly two days, leaving would-be customers -- and existing subscribers who want to upgrade -- in the lurch.

Reports of the outage first hit Twitter on Thursday, when current subscribers reported issues with online billing, upgrade eligibility checks, new phone activations and access to the carrier's My Verizon Web portal. The problem has not spilled over to the carrier's network, however, meaning users have full access to voice calls, data services and text messaging.

Verizon has since recognized the downtime, saying the problem is isolated to its online billing system and related services. In a statement provided to Re/code, the carrier said impacted areas include the Northeast, Midwest and limited southern states. The company declined to offer an exact number of customers affected by the issue.

Since the problem began, users have seen online error messages or complete failures to recognize billing and account information. For example, many existing customers logging into the My Verizon Web portal are met with the message, "Some account actions are temporarily unavailable while we upgrade our systems."

The downtime is also affecting potential Verizon customers, as phone activation services are tied to the company's billing system. Would-be iPhone buyers, for example, are seeing error messages similar to the one above when attempting to make a purchase or line upgrade through the Online Apple Store.

At the time of this writing, the situation remains in flux as some are reporting a return to service, while others continue to see problems.

The cause of the issue is unknown, though Verizon made it a point to note that it has not been hacked.

It started on Wednesday. So this is the third day. They have ZERO idea what happened and why. Customer database goes casters-up? Pull the freaking backup instance and make it live. If that fails then you don't really know what happened.

Makes me think of an article about how Amazon and Google are killing IBM because they are now the biggest suppliers of data services but use much cheaper hardware. Just sounds like a disaster waiting to happen.

On vacation with MBP, AT&T iPhone5, & Verizon iPad. I chose Verizon to be sure I had coverage if AT&T didn't, which often was Edge service only in some areas until last fall. I never use/trust public wifi, & use the iPad both directly & as a hub for the MBP.

Purchased 6gigs for $50 on Wed; transaction shows pending. My credit card was charged $.01 test charge, but not full transaction. IPad shows 6144 data balance "pending transaction," with no data still as of Friday night midnight. Doing everything on the iPhone at this point. Glad I can, but hard on older eyes.

I can view my data usage, but now I don't know if I should believe it. And how can I believe Verizon is correctly recording my usage at the end of the billing cycle? What if they claim I have 4GB of overage?